1. Technical Field
The present invention relates to a computer aided design system and a computer aided design program which transform the shape of a member into an objective curved surface shape.
2. Background Art
Today, there is a desire to shorten processes from planning to design and production to respond to consumer demand. In order to improve the efficiency of design and production processes, the use of CG (Computer Graphics) and CAD (Computer Aided Design) systems is popular. In order to depict shapes having complex curved lines or curved surface shapes, such as for motor vehicles, domestic electric appliances, or the like, on a computer, the following processing methods have conventionally been used.
The first method is solid modeling, where simple shapes called primitives are held in a computer, and operations to combine the shapes with each other are repeated in order to express complex shapes. A primitive is for example a column, a cube, a hexahedron, a torus, a ball, or the like, and in solid modeling shapes are represented by set operations on these primitives. Therefore, in order to produce a complex shape many steps are required and precise calculations are required.
The second method is surface modeling, which utilizes an algorithm such as a bezier, b-spline, rational bezier, NURBS (Non-Uniform Rational b-spline), or the like in order to perform operations such as cutting or connecting lines or surfaces, and by repeating these operations complex free curved lines or curved surfaces are represented.
However, even with a model in which there are no problems in the representation with the solid model or surface model described above, in some cases problems may occur when the model is used by a downstream application such as CAM, CAE, or the like. This is caused by differences between the support element to be supported by the produced computer graphics, and the support element to be supported by the other computer graphics, computer aided design, and downstream applications, and differences in shape definition, or the like. The model is corrected via an application such as a translator which modifies these differences (Japanese Unexamined Patent Publication Nos. 2001-250130, Hei 11-65628, Hei 10-69506, Hei 4-134571, Hei 4-117572, and Hei 1-65628).